1. Field of the Invention
The present invention relates to a battery remaining capacity measuring apparatus, more particularly to a battery remaining capacity measuring apparatus wherein the quantity of collected samples for battery current and voltage and the quantity of samples for obtaining averages thereof are determined depending on a discharging time of the battery.
2. Description of the Related Art
Generally, measurement of the battery remaining capacity of an electric automobile is premised that discharge is continued for at shortest 10 seconds as shown in FIG. 7 by keeping an accelerator pressed, as described in Japanese Patent Application Laid-Open No.H8-62310.
In the battery remaining capacity measuring apparatus disclosed in Japanese Patent Application Laid-Open No.H8-62310, discharge current I and voltage V from the battery are sampled every 1 millisecond, and each time when 100 units (N1) of this current value and voltage value of 1 millisecond are collected, those values are averaged so as to obtain average data. When 100 units (N2) of this average data (N1.times.N2=10000) are obtained, a correlation between current and voltage is obtained. When a strong negative correlation is indicated, an approximate line (Y=a.multidot.X+b Y: current, X: voltage) is obtained based on the 100 average data. Then, by substituting a specified value for Y in this equation, the voltage X is specified so as to regard this voltage as current remaining capacity. That is, the remaining capacity is obtained based on data obtained by measuring for 10 seconds.
Because the quantity of data is very massive, even when current data in a charging direction for a short time exists, this can be buried as an error.
However, recently, a high voltage vehicle called hybrid car or simple hybrid car has been used which contains two kinds of driving sources, namely an engine and a DC motor and is driven by an engine or DC motor.
In such a hybrid car, recharge and discharge to the battery are repeated frequently. Therefore, the quantity of current data in the recharging direction increases so that this cannot be neglected as an error.
Particularly at the time of regenerative charge during a traveling of a vehicle or generative charge with an alternator, charging current to the battery is not constant (constant voltage charge), so that the correlation between current and voltage is reduced.
That is, the aforementioned method in which each time when 100 (N1) units of data comprised of current value and voltage value of 1 millisecond are collected, those values are averaged so as to obtain average data and then when 100 (N2) units (N1.times.N2=10000) of this average data are obtained, a remaining capacity is obtained with the obtained current and voltage, cannot be applied to measurement of the remaining capacity of the hybrid car because the correlation therebetween is small when no specific measure is taken.